I agree. I work in criminal justice, you can examine the nature/nurture, the early beginnings, trauma etc etc etc until you’re blue in the face. Ultimately, some people just can’t function in a decent society, be rehabilitated or just be a decent human being, so should be kept away from those who can function ‘correctly’. At those ages you know that’s a horrific, unacceptable way to behave, if you don’t you need to be kept apart from society until you do. ‘Child’ or otherwise.
If the above requires building more prisons so be it. Or keep them in for longer. That doesn’t equate to no prison based work, if humans can be rehabilitated to come out nice functioning humans then great, but the majority can’t. Why should families go through this pain?